---
title: "SMR Hard Drives: WD, Seagate, Toshiba Models Explained - EXALAB"
description: "SMR (shingled magnetic recording) in WD, Seagate, Toshiba drives. The 2020 WD Red affair, WD Red Plus, and what SMR means for data recovery from your drive."
url: "https://www.exalab.cz/en/blog/smr-hard-drives-wd-seagate-toshiba-explained"
date: "2026-05-21T18:18:30+00:00"
language: "en-GB"
---

##  SMR Hard Drives: WD, Seagate, Toshiba Models Explained

*Updated in May 2026. This article was originally published in 2020 in response to the then-ongoing WD Red SMR controversy. We have added the development of the situation from 2020 to the present, the current list of affected models, a practical procedure for checking whether your drive uses SMR, and a section on what SMR means for data recovery. The technical explanation of the recording principle remains unchanged—physics hasn’t changed.*

SMR-related inquiries come into our lab on a continuous basis, year after year. Clients most often ask whether the technology might apply to their particular drive, or why their RAID array unexpectedly slowed down or got stuck during a rebuild. For some use cases—especially RAID arrays and NAS units—SMR may not be the right fit, which is why it is worth understanding what SMR actually is and which drives are affected.

  ![  SMR Hard Drives: WD, Seagate, Toshiba Models Explained](https://www.exalab.cz/images/blog/SMR-fw-1200x630.jpg) SMR stands for Shingled Magnetic Recording. It is used in conventional hard disk drives (HDDs) and works by partially overlapping the recorded tracks, much like shingles on a roof. Manufacturers use this technology as one of several ways to increase the amount of data that fits on the platter surface. **SMR may not be suitable for applications involving random writes**—typically RAID arrays or NAS units, where some form of RAID is usually present. A regular user who keeps an SMR drive as an external backup for photos often does not even know the drive is SMR, and in that scenario it may not be a problem at all. In more demanding scenarios, however, it can be.

 [data recovery from all types of storage media](https://www.exalab.cz/index.php?option=com_content&view=article&id=11:contact&catid=2)

A bit more concretely: write heads use a wider track width for writing than is actually necessary for subsequent reading. This is dictated by technological constraints. Read heads, by contrast, can do with reading from a narrower track. Drives using conventional recording (CMR—Conventional Magnetic Recording) place tracks side by side, which in theory wastes platter space because part of each track is unused from the read perspective. SMR is built precisely on using this unused space.

From a reading standpoint, this works fine. Writing, however, is a different story—and that is the catch. If part of the data is deleted and the drive subsequently writes new data to the same location, it has to somehow deal with the data still occupying part of the deleted-data tracks. Dealing with that can take some time. Users and certain devices do not appreciate the delay.

## How the drive handles it—cache and background reorganization

SMR drives set aside a special area on the platter that operates in conventional (CMR) mode and serves as a **media cache**. Incoming writes go here first. Then, during idle moments when the drive has nothing else to do, data is gradually migrated into the shingled zones, where—due to track overlap—entire groups of tracks must be rewritten at once. If a user wants to change a single sector within such a zone, the drive must first read all overlapping tracks above it, modify the relevant portion, and rewrite the whole bundle back. This operation is known as Read-Modify-Write, and on SMR drives it is a necessary part of normal operation.

As long as the drive has enough quiet moments between writes, the user notices nothing. Trouble starts when the media cache fills up faster than the drive can clear it into the shingled zones. At that point, write speed drops sharply—from the usual hundred-plus megabytes per second, speeds can fall to single-digit megabytes. The drive stops responding to further requests in time, and in some scenarios—typically during a RAID rebuild—the controller flags it as faulty and drops it from the array.

## Why this is a problem in RAID arrays and NAS units

A RAID rebuild is exactly the kind of scenario SMR resists with all its might. After a failed drive has been replaced, data computed from parity information on the remaining drives is written to the new drive continuously for hours, sometimes tens of hours. An SMR drive in this situation quickly exhausts its media cache and ends up in a state where it cannot keep up. The combination of delays, fluctuating latency, and occasional timeouts leads the NAS or RAID controller to eject the drive from the array. If another drive in the array starts misbehaving at that moment, the situation can escalate into data loss—even though the SMR drive itself may not be faulty at all; it simply could not handle the required workload.

This is why SMR drives in RAID arrays—particularly RAID 5 and RAID 6—rank among the riskiest configurations we encounter in the lab. It is not a theoretical threat. A failed rebuild involving SMR drives is a recurring scenario in practice.

## The 2020 WD Red controversy—how it all started

In April 2020, it came to light that **Western Digital was using SMR in the WD Red line**, a series primarily intended for NAS use. The drives in question were WD Reds with capacities from 2 TB to 6 TB carrying the model designation **WDxxEFAX**. WD Red Pro did not have this hidden property, nor did older WD Red models.

WD responded on its blog by explaining that WD Red drives used a different variant of SMR than the high-capacity drives intended for data centers. WD Red and the other consumer lines mentioned here used a technology called **DM-SMR** (Device-Managed SMR—shingled recording controlled by the drive itself), whereas data center drives use **Host-Managed SMR**, where control is handed to a dedicated host protocol (a server, for example). According to WD’s statement, the drive was supposed to perform operations related to shingled recording during idle periods, so neither the user nor the user’s equipment would need to worry about anything in practice.

In the real world, however, DM-SMR-equipped drives behaved differently. According to reports from various sources online, some users had problems with RAID array rebuilds after one drive failed and was replaced with a new DM-SMR drive. The rebuild took disproportionately long or ended in error.

Other WD drives equipped with DM-SMR include the 3.5" **WD Blue** 2 TB WD20EZAZ and 6 TB WD60EZAZ, the 2.5" **WD Blue** 1 TB WD10SPZX and 2 TB WD20SPZX, and the 2.5" **WD Black** 1 TB WD10SPSX.

Initially it looked like only Western Digital had pulled this “stealth upgrade” on some of its drives. A few days later, however, it turned out that Seagate and Toshiba were not in the clear either. **Seagate** had equipped the 5 TB Seagate Desktop ST5000DM000 with SMR, along with the Seagate Barracuda 4 TB ST4000DM004, Seagate Barracuda 8 TB ST8000DM004, and Seagate Barracuda 2 TB ST2000DM008.

**Toshiba** applied SMR to drives in the P300 series, specifically the 4 TB HDWD240UZSVA and 6 TB HDWD260UZSVA. P300 drives with capacities of 1 TB, 2 TB, and 3 TB should not be affected. Among 2.5" drives, SMR is used in the L200 MQ04 series—1 TB with 7 mm thickness and 2 TB with 9.5 mm thickness.

## What happened next—developments from 2020 to 2026

The controversy had several follow-ups worth mentioning, as they explain why we keep returning to SMR and NAS to this day:

**Class action lawsuits and settlement.** Several class action lawsuits were filed in the United States against Western Digital over misleading WD Red marketing. The court approved a settlement in December 2021—it was not significant financial compensation per drive, but rather a remedy of communication practices and more transparent product labeling.

**The launch of WD Red Plus.** Western Digital, in response to the controversy, introduced the **WD Red Plus** line in June 2020 as a CMR alternative to the basic Red line. This clarified the lineup: Red Plus and Red Pro are CMR (suitable for NAS), and **the basic WD Red line continues to use SMR in current production**. For a new NAS, then, the rule today is clear—pick Red Plus or Red Pro, not the basic Red.

**Greater manufacturer transparency.** After 2020, all three manufacturers (WD, Seagate, Toshiba) gradually started listing the recording type (CMR/SMR) directly in datasheets and product documentation. Western Digital and Seagate today maintain public lists of their drives with recording type. CMR/SMR can therefore be verified before purchase—something that was not a given in 2020.

**Spread of SMR across the consumer lineup.** What has not changed since 2020—or has rather gotten worse—is the overall spread of SMR. Today, SMR is more common than CMR in the consumer class. The vast majority of new 2.5" drives (internal and external) are SMR, most external 3.5" drives are too, and for 3.5" internal consumer drives, CMR and SMR variants exist in parallel. CMR today is found practically only in enterprise lines (WD Ultrastar, Seagate Exos, Toshiba MG), NAS-specific drives (WD Red Plus and Pro, Seagate IronWolf and IronWolf Pro, Toshiba N300), and older models roughly up to 2017.

For more detail on which lines from individual manufacturers use SMR and how that affects cases in our lab, see our summaries: [**Data Recovery from Western Digital Drives**](https://www.exalab.cz/index.php?option=com_content&view=article&id=160&catid=17), [**Data Recovery from Seagate Drives**](https://www.exalab.cz/index.php?option=com_content&view=article&id=161&catid=17), and [**Data Recovery from Toshiba Drives**](https://www.exalab.cz/index.php?option=com_content&view=article&id=168&catid=17).

## Why deleted-data recovery from SMR is complicated

On conventional drives using CMR or PMR recording, deleted file data physically remains on the platter until it is overwritten by new data. The operating system merely frees the entry in the file system table. That is why software recovery of deleted files from CMR drives often has a decent chance of success, as long as the drive is not used further right away.

On SMR drives, the situation is fundamentally different. The drive maintains its own internal map of what is in the media cache, what has been migrated into the shingled zones, and what can be rewritten as part of optimization from the firmware’s perspective. As soon as the drive gets a chance to work—even just a few minutes after files have been deleted—it begins to **reorganize data in the background**: moving content from cache into zones, cleaning tracks, optimizing layout. During this process, **deleted data may be permanently overwritten** without the user doing anything. The only requirement is that the drive is powered on.

For practical purposes, this means two things:

- **If you have accidentally deleted data from an SMR drive, power down the device immediately.** Each additional minute of runtime increases the risk that the drive will overwrite the deleted data during an idle moment. The classic advice of “disconnect the drive and do not use it further” applies even more strongly to SMR than to CMR.
- **The chances of software recovery of deleted data from SMR are significantly lower than for CMR.** Professional recovery is often the right path, where during work on the case we can disable internal drive functions that would otherwise progressively overwrite the deleted data.

It is worth clarifying that this mechanism is **not called TRIM**. TRIM is a function of flash memory (SSDs, memory cards, mobile phones) with a technically different principle—the flash media controller, upon receiving the TRIM command, removes the cells from inventory and resets them as part of Garbage Collection. On an SMR hard drive, the process is about reorganizing magnetic recording, not about clearing memory cells. The consequence for the user—“deleted data may be gone faster than you would think”—is, however, similar.

## Data recovery from SMR drives in our lab

SMR drives today make up a significant share of the cases we receive. External 2.5" drives such as WD My Passport, WD Elements, Seagate Expansion, and Backup Plus, as well as internal WD Blue 2 TB, Seagate Barracuda 4 TB, or Toshiba P300 6 TB—these are all models we routinely encounter. The recovery procedure on SMR differs from a classic CMR drive in several respects:

**During case work, we disable certain internal drive functions.** Every SMR drive starts its routine immediately on power-up: moving data from media cache into shingled zones, optimizing layout. If the drive has faulty read heads or damaged platter surface, this automatic activity can cause further, irreversible damage. As part of case work, we therefore use specialized tools (PC-3000 and others) to modify the drive’s service data so that these processes stay disabled throughout the entire reading operation. This is an intervention that requires specific hardware and software apparatus and cannot be performed in a regular IT shop.

**We work with the drive’s internal map.** SMR drives have, alongside the regular logical address map, a second-level map that tracks which data is currently in cache and which has been migrated to the zones. This map is stored in the drive’s service area and can become damaged on unexpected shutdown, power loss during reorganization, or a firmware error. For a drive that reports its correct capacity to the user but returns only zeros instead of data, damage to this map is a typical cause. Standard recovery software fails in such a case—specialized tools and procedures are required.

**Recovery chances depend on when and in what condition the drive arrives.** A drive that comes to us after a single failed read attempt and immediate power-down has a significantly higher chance than one a user has spent hours trying to connect, format, or “fix” with various utilities. This applies to all drives, but especially to SMR—every unnecessary cycle can trigger irreversible changes in the service area.

We will tell you the specific likelihood of data recovery only after free diagnostics. The price of data recovery starts at CZK 1,500 for individual drives and at CZK 2,500 for RAID arrays and NAS units. The final amount depends on the extent of damage and technical complexity. **You always pay only for successfully recovered data.**

## Should I check whether my drive uses SMR or not?

It depends on how you use the drive. If the drive sits in a regular home PC as standalone storage and has shown no unusual problems so far, there is no reason to act. SMR on its own is not a defect—the drive may serve faithfully for years; it just has a different behavior profile under random writes.

**Where you do want to address SMR:**

- **NAS and RAID arrays**—if you have a basic WD Red, WD Blue, Seagate Barracuda, or Toshiba P300 in your NAS or RAID array and you are considering expanding or replacing a drive, we recommend considering a switch to a CMR variant (WD Red Plus/Pro, Seagate IronWolf or IronWolf Pro, Toshiba N300). During a rebuild after a drive failure, SMR can behave unpredictably.
- **Before buying a new drive for a NAS**—verify the recording type in the datasheet or on the manufacturer’s public list (both WD and Seagate maintain such lists today). If it is not explicitly CMR, assume it is SMR.
- **If your drive uses SMR and starts behaving strangely**—slow responses, long waits when copying large files, unusual delays—do not keep stressing it with further attempts. An SMR drive in a problematic state tolerates load even worse than CMR.

How to verify SMR/CMR for a specific model:

- **Manufacturer’s datasheet**—on newer models, the recording type is now typically listed directly in the technical specifications.
- **Public lists from WD and Seagate**—both manufacturers published lists of drives with recording type after the 2020 controversy. Just find your model number (for example, WD20EFAX or ST4000DM004) and look it up.
- **Specialized databases**—community-maintained CMR/SMR drive overviews (for example, on Reddit’s r/DataHoarder or on independent technical sites) tend to be exhaustive even for older models.

If you are unsure whether your drive uses SMR, or if you are dealing with a drive that is behaving unusually, use our [free diagnostics](https://www.exalab.cz/index.php?option=com_content&view=article&id=11:kontakty&catid=2:zachrana-dat&Itemid=200#contactnumbers). We will check the condition of the specific drive and recommend the next steps.

For deeper context, our thematic pillars may also be useful:

- [**Data Recovery from Hard Disk Drives (HDD)**](https://www.exalab.cz/index.php?option=com_content&view=article&id=72&catid=2&Itemid=711)—a general overview of data recovery from HDDs of all brands and types.
- [**Data Recovery from NAS**](https://www.exalab.cz/index.php?option=com_content&view=article&id=372&catid=2&Itemid=826)—specifics of network attached storage, including WD My Cloud, Synology, and QNAP.
- [**Data Recovery from RAID Arrays**](https://www.exalab.cz/index.php?option=com_content&view=article&id=370&catid=2&Itemid=825)—a complete guide to RAID array recovery, including rebuilds involving SMR drives.
- SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá. Jeho využití je však vhodné spíš pro dlouhodobé zálohy a pod., kdy data nejsou často přepisována.

     [SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.](https://www.exalab.cz/images/igallery/resized/1-100/seagate_smr_vs_conventional_hard_drive_writing-94-800-600-80.jpg) ![SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.]( "SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.")
- Takto prezentuje SMR firma Western Digital.

     [Takto prezentuje SMR firma Western Digital.](https://www.exalab.cz/images/igallery/resized/1-100/smr_hdd_architecture-95-800-600-80.jpg) ![Takto prezentuje SMR firma Western Digital.]( "Takto prezentuje SMR firma Western Digital.")
- Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. Již 6. generace technologie HelioSeal a SMR je předurčuje pro datová úložiště určená především pro zálohy, kdy nedochází k častému přepisování dat.

     [Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ](https://www.exalab.cz/images/igallery/resized/1-100/ultrastar_dc_hc600_product_image-97-800-600-80.png) ![Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ]( "Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ")

- [ ![SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.](https://www.exalab.cz/images/igallery/resized/1-100/seagate_smr_vs_conventional_hard_drive_writing-94-120-90-80-c.jpg "SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.") ](https://www.exalab.cz/javascript:void(0);)
- [ ![Takto prezentuje SMR firma Western Digital.](https://www.exalab.cz/images/igallery/resized/1-100/smr_hdd_architecture-95-120-90-80-c.jpg "Takto prezentuje SMR firma Western Digital.") ](https://www.exalab.cz/javascript:void(0);)
- [ ![Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ](https://www.exalab.cz/images/igallery/resized/1-100/ultrastar_dc_hc600_product_image-97-120-90-80-c.png "Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ") ](https://www.exalab.cz/javascript:void(0);)

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 [](#) [](#)- [ ![SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.](https://www.exalab.cz/images/igallery/resized/1-100/seagate_smr_vs_conventional_hard_drive_writing-94-120-90-80-c.jpg "SMR - Shingled Magnetic Recording. Šindelový zápis dat dělá přesně to, co z názvu vyplývá.") ](https://www.exalab.cz/javascript:void(0);)

- [ ![Takto prezentuje SMR firma Western Digital.](https://www.exalab.cz/images/igallery/resized/1-100/smr_hdd_architecture-95-120-90-80-c.jpg "Takto prezentuje SMR firma Western Digital.") ](https://www.exalab.cz/javascript:void(0);)
- [ ![Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ](https://www.exalab.cz/images/igallery/resized/1-100/ultrastar_dc_hc600_product_image-97-120-90-80-c.png "Disky Ultrastar HC650 a HC620, které disponují kapacitou 20 TB a 14 TB. ") ](https://www.exalab.cz/javascript:void(0);)

 [](https://www.exalab.cz/javascript:void(0)) [](https://www.exalab.cz/javascript:void(0))

   Details   By František Fridrich  František Fridrich  [Blog](https://www.exalab.cz/en/blog)

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